MAZZAROPPI, Antonio (F & C s.r.l, Via Nicolo Copernico 28, Pomezia-Roma, I-00040, IT)
| CLAIMS
1. Method for the control of the temperature profile of glass sheets (500) passing through a furnace (1000) comprised in a heating horizontal plant, in particular for glass tempering, the furnace (100) being provided with lower heating elements (200) and upper heating elements (100) respectively placed below and above the horizontal line of passage of the glass sheets (500), the method being characterised in that:
- the upper heating elements (100) and/or the lower heating elements (200) are placed modularly in the two directions to cover the heating surface of the furnace (1000) and are individually controlled;
- for each upper (100) and/or lower (200) heating element the temperature value is continuously detected respectively by one or more corresponding upper (160) and/or lower (260) thermocouples in a zone that, when a glass sheet (500) is travelling in front of the upper and/or lower heating element (100), is in the proximity of the glass sheet (500) surface facing the relevant upper (100) and/or lower (200) heating element,
- each upper (100) and/or lower (200) heating element is activated and regulated with respect to the heating power on the basis of said detected temperature value; so that each upper (100) and/or lower (200) heating element is activated only when a glass sheet (500) travels in front of it and regulated with a power that is such as to obtain the desired heating of the zone covered by the same upper (100) and/or lower (200) heating element.
2. Method according to claim 1 , characterised in that the glass sheet heating relevant to each upper (100) and/or lower (200) module is additionally obtained by convection of air that is heated by the same heating element. 3. Method according to claim 1 or 2, characterised in that each upper heating element (100) is activated and regulated with respect to heating power on the basis of the value of the difference between the temperature detected by the said corresponding one or more upper thermocouples (160) and a corresponding predefined nominal value.
4. Method according to claim 3, characterised in that said predefined nominal value is equal for all the upper heating elements (100). 5. Method according to claim 1 or 2, characterised in that each upper heating element (100) is activated and regulated with respect to heating power on the basis of the time variation of said detected temperature value.
6. Method according to any claim 1 to 5, characterised in that: - each upper heating element (100) is only activated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more upper thermocouple (160) as specified in any claim 3 to 5,
- only one predefined upper heating element (100), called "upper master" is regulated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more upper thermocouples (160) as specified in any claim 3 to 5;
- each upper heating element (100), except the "upper master", is regulated on the basis of the values of the temperatures detected by the said corresponding one or more upper thermocouples and said one or more thermocouples of the upper master.
7. Method according to any claim 1 to 6, characterised in that:
- the lower heating elements (200) are of the same type of, in the same number of, and are placed specularly to the upper heating elements (100) to cover the heating surface of the furnace (1000), and are individually controlled;
- each lower heating element (200) is activated and regulated with respect to the heating power on the basis of the temperature value detected by the facing upper heating element (100); so that each lower heating element (100) is activated only when a glass sheet (500) travels above it and regulated with a power that is such as to obtain the desired heating of the zone covered by the same lower heating element (200).
8. Method according to any claim 1 to 6, characterised in that:
- the lower heating elements (200) are placed modularly in the two directions to cover the heating surface of the furnace (1000) and are individually controlled; - for each lower heating element (200) the temperature value is continuously detected, by one or more corresponding lower thermocouples (260), in a zone that is in the proximity of the glass sheet (500) surface facing the relevant lower heating element (200) when the glass sheet (500) is passing above the upper heating element (200),
- each lower heating element (200) is activated and regulated with respect to the heating power on the basis of said detected temperature value; so that each lower heating element (200) is activated only when a glass sheet (500) travels above it and regulated with a power that is such as to obtain the desired heating of the zone covered by the same lower heating element (200).
9. Method according to claim 8, characterised in that each lower heating element (200) is activated and regulated with respect to heating power on the basis of the value of the difference between the temperature detected by said corresponding one or more lower thermocouples (260) and a corresponding predefined nominal value.
10. Method according to claim 9, characterised in that said predefined nominal value is equal for all the lower heating elements (200). 11. Method according to claim 8, characterised in that each lower heating element (200) is activated and regulated with respect to heating power on the basis of the time variation of said detected temperature value.
12. Method according to claim 8, characterised in that: - each lower heating element (200) is only activated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more lower thermocouples (260) as specified in any claim 9 to 11 , - only one predefined lower heating element (200), called "lower master" is regulated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more lower thermocouples (260) as specified in any claim 9 to 11 ; each lower heating element (200), except the "lower master", being regulated on the basis of value of the difference between the temperature value detected by said corresponding one or more lower thermocouples and the temperature value detected by said one or more thermocouples of the lower master. 13. Method according to any claim 8 to 12, characterised in that each lower heating element (200) and each upper heating element (100) is activated and regulated with respect to heating power on the basis of a combination of the temperature values detected in the proximity of the two glass surfaces so that the lower heating element (200) and the upper heating element (100) are activated only when a glass sheet (500) travels in front of them and are regulated with such a power that one obtains the desired heating of the zone covered by the same lower heating element (200) and upper heating element (100).
14. Method accordino o any claim 1 to 13, characterised in that the temperature value for each upper (100) and/or lower (200) heating element is obtained by the combination of the values detected by more upper and/or lower thermocouples.
15. Apparatus for the control of the temperature profile of glass sheets (500) in a furnace (1000) provided with transport rollers (300) and comprised in a horizontal heating plant, in particular for glass tempering, such an apparatus comprising lower heating elements (200) and upper heating elements (100) for the heating of the glass sheets (500) along their horizontal path inside the furnace (1000), characterised in that: - the upper heating elements (100) and/or the upper heating elements (200) are a plurality of elements individually controllable and modularly disposed on a plane in the two principal directions so as to substantially cover the useful surface for the heating of glass sheets (500); each upper (100) and/or lower (200) heating element is respectively provided with one or more corresponding upper (160) and/or lower (260) thermocouples which protrudes from the same element and gets near to the zone of sliding of the glass sheets (500), - there are comprised in the apparatus means for the activation and the power regulation of said upper (100) and/or lower (200) heating elements, each upper (100) and/or lower heating element being activated and regulated, according to the method of any claims 1 to 5, with respect to heating power on the basis of the temperature value respectively detected by said corresponding upper and/or lower thermocouples (160), in such a way that the upper (100) and/or lower (200) heating element is activated only when a glass sheet (500) travels in front of it and with a power that is such as to obtain the desired heating of the zone covered by the same upper (100) and/or lower (200) heating element.
16. Apparatus accordino to claim 15, characterised in that each upper (100) and/or lower (200) heating element further comprises means for the convection of air heated by the same heating element.
17. Apparatus according to claim 16, characterised in that each upper heating element (100) comprises means for the blowing-in of the heated air on said glass sheets (500), said means comprising or being constituted by an input pipe (110) of compressed air, a coil (120), disposed on an upper plane but near to said upper and/or lower heating elements, for the heating of the compressed air, and nozzles (130) for the sending of the same air on the surface of the glass sheet (500).
18. Apparatus according to claim 17, characterised in that the compressed air feeding to said input pipe (110) is regulated by suitable frequency flow rate regulators (5000).
19. Apparatus according to any claim 15 to 18, characterised in that only one thermocouple (160,260) for each upper (100) and/or lower
(200) heating element is used, that respectively protrudes from the central region of the surface of each upper (100) and/or lower (200) heating element.
20. Apparatus according to any claim 15 to 19, characterised in that the lower heating elements (200) are constituted by air blowing-in pipes disposed transversely to the feeding direction of the glass sheets (500). |
Method and apparatus of controlled heating of glass sheets in a furnace, in particular for the tempering of the glass.
The invention concerns an apparatus and method of controlled heating of glass sheets in a furnace, in particular for the tempering of the glass.
More in detail, the method according to the invention allows the control of the temperature on the whole surface of the glass sheet, apart from the particular cause of lack of thermal homogeneity and feed direction of the glass sheet.
Method and apparatuses for the tempering of the glass are known in the prior art.
The patent EP 0564489 in the name of Tamglass Engineering Oy 1 filed on 20th of December 1991 , describes a method for equalising the temperature profile of glass sheets in a furnace provided with rollers on which the glass sheets slide, wherein, in an already known way, the glass sheets are exposed to radiative, convective and conductive effects on both faces, and the upper surface of the glass sheets undergoes an intensified air convection at least at the beginning of the glass heating step, by means of air blowing-in pipes placed over the glasses. The patent EP 0564489 introduces the novelty that the air blowing-in pipes (that are transversal with respect to the feed direction of the glass) are controlled individually or in groups so as they are activated only in the zone wherein the glass sheets is present. For this reason, a longitudinal position sensor of the input glass sheet is present, as well as a calculator which calculates the glass position on the basis of the movement imposed to the last. One can use single valves for groups of blowing-in pipes.
Such a solution does not allow to control the temperature of the single nozzles of the pipes, and therefore to guarantee a heating only where it is needed on the glass surface, nor it allows to control the transversal position of the glass. There is therefore no suitable control of the pre-heated air that is sent to the glass. The only thing that one obtains is to save energy where the glass is not present.
The patent EP 1377529 in the name of Glaverbel, filed on the 15th March 2002, describes a method for equalising the temperature profile of glass sheets in a furnace that is provided with rollers on which the glass sheets slide; in particular, according to the already known prior art, the glass sheets are exposed to radiative, convective and conductive effects on both faces, and further the lower surface and the upper surface of the glass sheets undergo a forced air convection. The novelty introduced by the patent is that on the lower surface of the sheets the air is blown in by means of slanting jets directed towards the glass, which form an ingle of at least 5° with respect to an axis transversal to the glass; moreover, the air jets are oriented in the feed direction of the glass sheets and the nozzles of the air jets directed in such a way that their symmetry axis cuts through the surface of the lower face of the sheets beyond the median of the distance that separates the symmetry axis of two subsequent rollers. This would allow, in an apparatus like that of the above mentioned patent EP 0564489, to increase the convection rate on the lower surface of the glasses in case of bending of the sheet due to a lack of heating homogeneity between lower surface (in contact with the transport rollers) and the upper surface. Indeed, when the glass bends, and therefore does not fully contact any longer the rollers, and the air jet is not perpendicular but slanting, the lower surface that is subjected to this jet is larger than in the case of perpendicular jets. The final effect would be the elimination of the glass bending due to the lack of upper/lower heating homogeneity.
This solution would allow therefore to eliminate a cause of the glass bending. There exists however many causes, i.e. many lack of heating homogeneity, also due to temporary malfunctions, and therefore there is still the need of a method which eliminates all the causes, that is which allows a control on the whole upper and lower surface of the glass, without the need of adding a different expedient for each different cause that is described in the process in the course of time. This also because, together with the refining of the techniques, the additional control of the small lacks of homogeneity or the temporary lacks of homogeneity becomes more and more difficult.
It is object of the present invention a method of heating of glass sheets in a furnace, which solves the problems and goes beyond the drawbacks of the prior art.
It is subject-matter of the present invention a method for the control of the temperature profile of glass sheets passing through a furnace comprised in a heating horizontal plant, in particular for glass tempering, the furnace being provided with lower heating elements and upper heating elements respectively placed below and above the horizontal line of passage of the glass sheets, the method being characterised in that:
- the upper heating elements and/or the lower heating elements are placed modularly in the two directions to cover the heating surface of the furnace and are individually controlled;
- for each upper and/or lower heating element the temperature value is continuously detected respectively by one or more corresponding upper and/or lower thermocouples in a zone that, when a glass sheet is travelling in front of the upper and/or lower heating element, is in the proximity of the glass sheet surface facing the relevant upper and/or lower heating element, - each upper and/or lower heating element is activated and regulated with respect to the heating power on the basis of said detected temperature value; so that each upper and/or lower heating element is activated only when a glass sheet travels in front of it and regulated with a power that is such as to obtain the desired heating of the zone covered by the same upper and/or lower heating element.
Preferably according to the invention, the glass sheet heating relevant to each upper and/or lower module is additionally obtained by convection of air that is heated by the same heating element. Preferably according to the invention, each upper heating element is activated and regulated with respect to heating power on the basis of the value of the difference between the temperature detected by the said
corresponding one or more upper thermocouples and a corresponding predefined nominal value.
Preferably according to the invention, said predefined nominal value is equal for all the upper heating elements. Preferably according to the invention, each upper heating element is activated and regulated with respect to heating power on the basis of the time variation of said detected temperature value.
Preferably according to the invention,:
- each upper heating element is only activated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more upper thermocouple as above specified,
- only one predefined upper heating element, called "upper master" is regulated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more upper thermocouples as above specified;
- each upper heating element, except the "upper master", is regulated on the basis of the values of the temperatures detected by the said corresponding one or more upper thermocouples and said one or more thermocouples of the upper master.
Preferably according to the invention:
- the lower heating elements are of the same type of, in the same number of, and are placed specularly to the upper heating elements to cover the heating surface of the furnace, and are individually controlled;
- each lower heating element is activated and regulated with respect to the heating power on the basis of the temperature value detected by the facing upper heating element; so that each lower heating element is activated only when a glass sheet travels above it and regulated with a power that is such as to obtain the desired heating of the zone covered by the same lower heating element. Preferably according to the invention:
- the lower heating elements are placed modularly in the two directions to cover the heating surface of the furnace and are individually controlled;
- for each lower heating element the temperature value is continuously detected, by one or more corresponding lower thermocouples, in a zone that is in the proximity of the glass sheet surface facing the relevant lower heating element when the glass sheet is passing above the upper heating element,
- each lower heating element is activated and regulated with respect to the heating power on the basis of said detected temperature value; so that each lower heating element is activated only when a glass sheet travels above it and regulated with a power that is such as to obtain the desired heating of the zone covered by the same lower heating element. Preferably according to the invention, each lower heating element is activated and regulated with respect to heating power on the basis of the value of the difference between the temperature detected by said corresponding one or more lower thermocouples and a corresponding predefined nominal value. Preferably according to the invention, said predefined nominal value is equal for all the lower heating elements.
Preferably according to the invention, each lower heating element is activated and regulated with respect to heating power on the basis of the time variation of said detected temperature value. Preferably according to the invention:
- each lower heating element is only activated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more lower thermocouples (260) as above specified, - only one predefined lower heating element, called "lower master" is regulated with respect to heating power on the basis of the value of the temperature detected by said corresponding one or more lower thermocouples as above specified;
each lower heating element, except the "lower master", being regulated on the basis of value of the difference between the temperature value detected by said corresponding one or more lower thermocouples and the temperature value detected by said one or more thermocouples of the lower master.
Preferably according to the invention, each lower heating element and each upper heating element is activated and regulated with respect to heating power on the basis of a combination of the temperature values detected in the proximity of the two glass surfaces so that the lower heating element and the upper heating element are activated only when a glass sheet travels in front of them and are regulated with such a power that one obtains the desired heating of the zone covered by the same lower heating element and upper heating element.
Preferably according to the invention, the temperature value for each upper and/or lower heating element is obtained by the combination of the values detected by more upper and/or lower thermocouples..
It is further specific subject-matter of the invention an apparatus for the control of the temperature profile of glass sheets in a furnace provided with transport rollers and comprised in a horizontal heating plant, in particular for glass tempering, such an apparatus comprising lower heating elements and upper heating elements for the heating of the glass sheets along their horizontal path inside the furnace, characterised in that: the upper heating elements and/or the upper heating elements are a plurality of elements individually controllable and modularly disposed on a plane in the two principal directions so as to substantially cover the useful surface for the heating of glass sheets; each upper and/or lower heating element is respectively provided with one or more corresponding upper and/or lower thermocouples which protrudes from the same element and gets near to the zone of sliding of the glass sheets, there are comprised in the apparatus means for the activation and the power regulation of said upper and/or lower heating elements,
each upper and/or lower heating element being activated and regulated, according to the method subject-matter of the invention, with respect to heating power on the basis of the temperature value respectively detected by said corresponding upper and/or lower thermocouples, in such a way that the upper and/or lower heating element is activated only when a glass sheet travels in front of it and with a power that is such as to obtain the desired heating of the zone covered by the same upper and/or lower heating element.
Preferably according to the invention, each upper and/or lower heating element further comprises means for the convection of air heated by the same heating element.
Preferably according to the invention, each upper heating element comprises means for the blowing-in of the heated air on said glass sheets, said means comprising or being constituted by an input pipe of compressed air, a coil, disposed on an upper plane but near to said upper and/or lower heating elements, for the heating of the compressed air, and nozzles for the sending of the same air on the surface of the glass sheet.
Preferably according to the invention, the compressed air feeding to said input pipe is regulated by suitable frequency flow rate regulators. Preferably according to the invention, only one thermocouple for each upper and/or lower heating element is used, that respectively protrudes from the central region of the surface of each upper and/or lower heating element.
Preferably according to the invention, the lower heating elements are constituted by air blowing-in pipes disposed transversely to the feeding direction of the glass sheets.
The invention will be now described by way of illustration but not by way of limitation according to its preferred embodiments, making reference to the drawings of the enclosed figures, wherein:
- figure 1 shows a view of an embodiment of the apparatus according to the invention;
- figure 2 shows a detail of an embodiment of the apparatus according to the invention;
- figure 3 shows a further view of an embodiment of the apparatus according to the invention; - figure 4 shows an embodiment of the apparatus according to the invention.
In the following, the expression heating module will be used both to indicate the whole heating module of the glass sheets, to be included in the whole of the furnace for glass, and a single heating module which is arranged to heat only a zone of the glass sheet. The difference will be evident thanks to the context.
As known in the prior art, for example in an apparatus for the tempering of the glass there are upper modules and lower modules for the radiative and convective heating of the glass sheets which slide longitudinally at the centre of the apparatus, on suitable rollers.
In the following, the invention will be mainly illustrated with respect to the upper module, but the same tecnical features can be embodied even only in the lower modules.
Making reference to figure 1 , the upper heating modules 100 according to the invention are illustrated.
The compressed air enters through the input duct 110 and passes through a horizontal coil 120, which contacts the ceramic material 140 which supports resistances 150. In such a way, the air is pre-heated. One remarks that the ceramic material is shaped so as to leave uncovered the part of the resistances 150 turned to the glass sheet and rollers (not shown).
The so pre-heated air is made flowing out in the direction of the glass sheets through the nozzles 130, in the particular embodiment illustrated six nozzles per module. In figure 2, one shows from above the composition of the upper modules 100. Only four of them are illustrated for the sake of simplicity. For each module the coils 120 are visible. Each module is therefore powered and heated independently from the other modules. It is here to
be specified that the modularity of the heating is on the two direction of the surface to be heated, therefore both horizontally and transversely at least two modules are present.
Making reference to figure 3, one observes thermocouples 160 indicated in figure 2 as well. These thermocouples serve to detect the temperature of the glass sheet (not shown) which passes through the furnace on the rollers 300. In such a way, one can heat each module 100 as a function of the glass temperature detected in the zone of the glass sheet corresponding to the area projected by the heating module 100. The thermocouples are used at the same time to detect the presence itself of the glass sheet.
Indeed, the glass sheet is to be heated and therefore it will be always at a temperature lower than the pre-defined nominal temperature for the module 100. Additionally, one can define one of the modules 100 as a master module, for example at the centre of the furnace (whole heating module). Only with respect to this master module, the heating power will be regulated during time on the basis of the temperature difference between the thermocouple and the predefined nominal temperature, whilst all the other modules 100 will refer to the temperature detected by the thermocouple of the master module in order to be able to regulate their heating power during time. Thus, one will be able to avoid temporal derivatives of the local temperature which are not coherent one with the other. In such a way, we can obtain a better equalisation of the temperature profile of the glass, and most of all a temporal progression of the rotation, which is more regular, rapid and accurate.
More specifically, there is a program which manages the power of each single module 100 in such a way to follow the progression of the heating of the master module. The thermocouple detects the temperature of the air, then, where there is the glass that absorbs heat, the air has a lower temperature, therefore the program, in order to follow the master
zone, provides more power to the interested zone. The power of a module 100 (module X) which is not the master module is given by:
P x is the power of the zone of module X T x is the temperature of the zone of module X Ts is the pre-defined nominal temperature P M is the power of the zone of master module T M is the temperature of the zone of master module
This can be done even when one uses a similar modules system for the heating of the lower surface of the glass.
This methodology with the master module can be applied also to the lower modules 200. In particular, the master can be chosen only among the upper modules or only among the lower modules.
As illustrated in the figure, there are also thermocouples 260 in the lower heating modules 200. The information coming from the lower thermocouple 260 can be used for the control of the lower heating modules 200, which can be even of different nature with respect to the upper ones 100, or this information can be combined with the information coming from the upper thermocouples 160 to steer the upper and/or lower modules so as to guarantee uniformity of heating of the glass sheets, or impress particular deformation to the same.
One stresses the fact that the lower modules 200 can also be constituted by pipes that are transversal to the glass feed direction (and comprising suitable nozzles for the blowing of the preheated air), as in the prior art, or be identical to the upper ones 100 according to the invention.
Making now reference to figure 4, one illustrates the whole heating module 1000, together with the compressed air feeding system. A compressor 2000 generates the compressed air, which then passes through a plenum chamber 3000 and arrives to distribution valves
4100 (for the lower modules), 4200, 4300 (for the upper modules). Starting
from this, then, the compressed air is directed towards one or more frequency low rate regulators 5000, which determines the quantity of air let in in the coils 120 and therefore sent to the glass sheets 500 through the nozzles 130, 230. The lower modules can be powered also by another known system, but the whole is particularly effective using the solution of the present invention applied to the lower modules as well.
An electronic central unit (not shown) elaborates the data coming from the thermocouples and steers the heating for each single (lower and/or upper) module. It is here to be specified thet even only upper heating elements or lower heating elements can be utilised. The last case is particularly adapted to the treatment of low-emissivity glasses, i.e. glasses with a covering material only the upper side. Indeed, in such a case the covering material reflects the rays and heats too rapidly with respect to what happens for the opposide side of the glass sheet, and therefore is convenient to measure the temperature in the neighbourhoods of the lower side.
In any case, the modularity of the lower heating elements can be particularly advantageous still in the low-emissivity glasses case, since in such a case the detection of the temperature can be more precise.
Indeed, the positioning of the upper thermocouple too near to the glass sheet surface would not be convenient, due to the fact that the covering layer can be of different thicknesses. Instead, one can position the lower thermocouple very close to the lower surface of the glass sheet, for example 8 mm close to it, and this allows a more precise detection of the temperature.
In the case of the lower heating modules, the thermocouple is positioned between the rollers and this allows precisely to get close to the glass surface as above specified. Finally, according to another embodiment, each lower and/or upper heating element can be provided by more thermocouples; indeed, the relevant temperature values can be combined and the combination can be utilised for the activation and/or regulation of the same element.
With the solution of the present invention one obtains the following advantages:
- zone-differentiated heating of the glass sheet, the zones resulting from a both transversal and longitudinal subdivision of the heating surface, arranging independent modules for each of such zones deriving from the subdivision;
- controlled uniform heating of the glass sheet;
- control of the upper and/or lower heating of the glass sheets, by detecting the temperature in the proximity of the same glass sheet in the working zone of the single heating module;
- utilisation of the radiative heating system for the pre-heating of the air destined to the convective heating.
The solution according to the present invention allows to go beyond, all in one go, the partial solution of the prior art, because it allows, by means of a different system, to control the heating of the glass on different zones of the same, and therefore to guarantee a uniformity of upper/lower, longitudinal/transversal heating of the glass sheet. Such a uniformity is not even remotely possible to reach by the devices of the prior art because of the relevant limited technical solutions which, if on one hand improve a heating mode, on the other hand introduce technical problems and limitations to the control of the heating.
The present invention has been described for illustrative but not limitative purposes, according to its preferred embodiments, but it is to be understood that modifications and/or changes can be introduced by those skilled in the art without departing from the relevant scope as defined in the enclosed claims.